Electrically controlled pumping of spin currents in topological insulators

Abstract

Pure spin currents are shown to be generated by an electrically controlled quantum pump applied at the edges of a topological insulator. The electric rather than the more conventional magnetic control offers several advantages and avoids, in particular, the necessity of delicate control of magnetization dynamics over tiny regions. The pump is implemented by pinching the sample at two quantum point contacts and phase modulating two external gate voltages between them. The spin current is generated for the full range of parameters. On the other hand, pumping via amplitude modulation of the interboundary couplings generates both charge and spin currents, with a pure charge current appearing only for special values of the parameters for which the Aharonov-Bohm flux takes integer values. Our setup can therefore serve to fingerprint the helical nature of the edges states with the zeros of the pumped spin and charge currents occurring at distinct universal locations where the Fabry-Pérot or the Aharonov-Bohm phases take integer values

Proposal for an on-demand source of polarized electrons into the edges of a topological insulator

“…27 It can be used for creating on-demand pure spin-current. [28][29][30][31][32] The Article is structured in the following way: we start by presenting the SpPS set-up (Sec. II), then we show the results for the emitted current and noise (Secs.…”

Noise and current correlations in tunnel junctions of quantum spin Hall edge states

“…In the central region of the setup, the two edge states are coupled by electron tunneling. The tunneling Hamiltonian that preserves time-reversal symmetry consists of two terms [29][30][31][32][33][34][35] , H tun =Ĥ p tun +Ĥ f tun , wherê…”

“…[24][25][26][27] For the helical states, a constriction in the QSH bar causes a local wavefunction overlap 28,29 that is known to yield two types of tunneling processes. [29][30][31][32][33][34][35][36][37][38][39] The first type is the customary spin-preserving (p) process, where an electron tunnels across the junction maintaining its spin orientation, and thereby reversing its group velocity. The second type is less conventional and is a spin-flipping (f ) process, where a tunneling electron reverses its spin orientation maintaining its group velocity: it mainly originates from the interplay between bulk-inversion asymmetry and wavefunction overlap, even in absence of magnetic coupling.…”

Electronic interference transport and its electron–phonon interaction in the Sb-doped Bi2Se3nanoplates synthesized by a solvothermal method

“…They showed that in the weak coupling limit, topological spin pumps are characterized by the appearance of symmetryprotected gapless end states during the pumping cycle, similarly to the Z 2 pump. Several different methods have been put forward to realize the Z 2 pump experimentally, including a Luttinger liquid [34], a double-corner junction in a topological insulator [35], and quantum wires proximity coupled to a superconductor [36].…”